A stream cipher is an encryption algorithm which encrypts arbitrary length plain text, using a (fixed length) key. Some stream ciphers generate a key stream from only the key, which is then XOR-combined with the plain text, others feed back plain text or cryptotext into the algorithm to create the ...

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How can I protect against the failure of a block or symmetric cipher?

Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of? Are some combination of ciphers ...
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2answers
478 views

are CFB and OFB really meant for streaming?

CFB, OFB and other modes are meant for streaming and don't require padding. Are there still limitations such as the text needs to be greater than key length?
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Simple xor cipher extension

Probably the simplest cipher is the xor cipher with a single integer. One can extend this to use more than one integer by several means. I'm wondering if there is any benefit to doing more than this: ...
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4answers
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Can you make a hash out of a stream cipher?

A comment on another question made me wonder about something: Assume you're on a rather constrained platform — say, a low-end embedded device — with no built-in crypto capabilities, ...
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1answer
96 views

Is the following scheme secure for different cipher

Let's say I have two keys K1 and K2. two messages M1 and M2 of the same length. Cipher (E,D) 3 ciphertexts: C11, C12,C22 where Cij = E(Ki, Mj) In situation ...
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4answers
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Stretching a random seed to maximize entropy

I'm using a random number generator that requires me to pass it a big (several kilobytes) pool of random data for initialization. I've gathered entropy from various system metrics (free memory, ...
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1answer
172 views

When is an asymmetric scheme considered broken?

Does the following quote imply that valid encrypted data can be created and decrypted by someone other than the owner of a private key: An asymmetric encryption scheme is considered to be broken ...
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3answers
650 views

Converting a stream cipher into a block cipher

The well-known Counter-Mode (CTR) mode of operation for a block cipher essentially converts any block cipher into a stream cipher. Is there a way to do the reverse? In other words, given a "good" ...
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Proof that Alternating Step Generator and modifed ASG' have equivalent security?

The Alternating Step Generator (ASG) is a PRNG combining 3 LFSRs. Output of the ASG is the XOR of the output of two clock-gated LFSRs. At each step, a single one of these LFSRs is clocked, according ...